Thermoplastic resins have been steadily extending their use in various fields, such as automobile parts, appliances parts, and office automation equipment parts, because of their superior moldability and impact resistance as compared with inorganic materials, such as glass.
In these fields, in order to produce large-sized and thin-walled articles and to reduce the molding cycle, there has been an increasing demand for thermoplastic resins to have improved flow.
Various additives for improving flow of thermoplastic resins have been proposed to date. For example, addition of a mineral oil, which has been industrially adopted for a long time, improves flow but, in turn, causes a considerable reduction in heat resistance. It has been proposed to compound a thermoplastic resin with an ester of a polyhydric alcohol and a fatty acid (see JP-A-61-231045 and JP-A-61-275341 (the term "JP-A" as used herein means an "unexamined published Japanese patent application")); a higher fatty acid and a metal salt thereof (see JP-A-62-132951); a higher fatty acid metal salt and a specific phosphorous ester (see JP-A-62-190242); a fatty acid amide or an aliphatic alcohol and ethylene-bis-stearamide (see JP-A-62-257951); an ester of a higher fatty acid and a higher alcohol (e.g., stearyl stearate) (see JP-A-2-135219); or an isocyanuric ester compound (see JP-A-2-194047). Some making only insufficient improvement in flow, or some seriously impairing the heat resistance of the resin, and none of them provides a satisfactory thermoplastic resin composition.
On the other hand, aromatic phosphoric esters, such as triphenyl phosphate and tricresyl phosphate, are known to be effective to improve flow of thermoplastic resins. However, they not only bring about a marked reduction in heat resistance but generate decomposition gases on injection molding. The decomposition gases are condensed and deposited on the wall of an injection mold, so-called "mold deposit" resulting in impairment of the appearance of the resulting molded articles.
For example, a resin composition comprising a vinyl aromatic resin, polyphenylene ether, an aromatic phosphoric ester, and a nitrogen-containing compound is disclosed in JP-A- 54-38348, JP-A-54-38349, and EP 311909. Mainly comprising polyphenylene ether of low flowability, the resin composition has poor moldability. Besides, use of the aromatic phosphoric ester (e.g., triphenyl phosphate) causes mold deposit and reduction in heat resistance.
A combination of a hydroxyl-containing aromatic phosphoric ester and a phenol resin is disclosed in JP-A-1-223158, but the publication gives no reference to a combination of the additive with a thermoplastic resin, still less expectation of improving flow of a thermoplastic resin while retaining heat resistance, impact resistance, and flame retardance.
Further, a polyester resin composition containing tris(hydroxyphenyl) phosphate is disclosed in JP-A-50-98956. However, since the organophosphorus compound used contains three hydroxyl groups per molecule, it has poor compatibility with polyester only to provide a resin composition having imbalance of heat resistance, flow, and impact resistance.